In 3.10 via PEP 604, there was an attempt to use the new union of types where runtime types were previously expected to be a tuple. `isinstance(x, (A, B))` can be written `isinstance(x, A | B)`. Unfortunately, there still is a case were a tuple of types is required: `except (A, B) as err:` cannot be written `except A | B as err:`. I think this should be allowed; it is consistent with isinstance and pattern matching's use of |, and nicely avoids confusion with `except A, B:` which is disallowed for Python 2 reasons; `except A | B`: would be valid.

This would be nice but I'm not sure it's worth the hassle in terms of documentation, tooling support, etc.

There is an existing issue (that I can't find right now) that makes the `except` machinery use `__instancecheck__`, instead of looking only at real base classes like it does now. That change would automatically also make `|` work.

I don't think that `except A|B` looks better than `except (A, B)`, so I am against this proposal. Exception matching is its own special thing (e.g. it doesn't honor virtual subclasses) and we shouldn't hyper-generalize.

> I don't think that `except A|B` looks better than `except (A, B)`

I agree.